build: fix VPATH testsuite

'make check' has been failing on VPATH builds since commit
907a39e7.  The tests already had magic for munging path names,
but were munging to the wrong location, thus working only on
an in-tree build.

* tests/securityselinuxlabeltest.c (testSELinuxMungePath): Munge
to correct path.

tests/securityselinuxlabeltest.c

 /*
- * Copyright (C) 2011-2012 Red Hat, Inc.
+ * Copyright (C) 2011-2013 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -61,7 +61,7 @@ testSELinuxMungePath(char **path)
     char *tmp;
 
     if (virAsprintf(&tmp, "%s/securityselinuxlabeldata%s",
-                    abs_srcdir, *path) < 0) {
+                    abs_builddir, *path) < 0) {
         virReportOOMError();
         return -1;
     }